The present invention relates to a servo valve, in particular to a two-stage or multistage electrohydraulic servo valve, in accordance with the preamble of claim 1.
Particularly high demands are today made on the operating behavior of the installed hydraulic components within a hydraulic system in hydraulic system engineering. The installed hydraulics should in particular regulate specific hydraulic volume flows or hydraulic volume pressures with high precision in accordance with predefined control signals. Valves suitable for this purpose, in particular continuous valves, allow a continuous transition of the switch positions of the valve to be permitted.
With continuous valves, an electrical input signal for controlling the continuous valve is accordingly converted into a hydraulic output signal. The long-known servo valves belong to a category of continuous valves and allow a highly precise and above all continuous setting of the valve switch position, which is in particular considered a basic requirement in modern aviation technology.
So-called two-stage electrohydraulic servo valves (EHSV) are known from the prior art which comprise a first stage, the so-called pilot stage, and a second stage, the so-called power stage. The power stage in this respect has a control slide valve which remains in its position or is moved depending on the pressures acting on it. The electrically controllable pilot stage can have an armature which rotates in dependence on a magnetic field and in this respect varies the pressure relationships at the control slide valve via a jet pipe principle. The deflection of the control slide valve is thereby effected, i.e. the pilot stage serves the controlling of the power stage, i.e. a controlled deflection of the control slide valve, by means of which a volume flow to a component to be controlled dependent on the position of the control slide valve is released or blocked or is set in its magnitude. The servo valves can selectively also be configured or work according to the jet pipe principle, flapper nozzle principle or the deflector jet principle or also according to any other possible operating principle.
Such an electrohydraulic servo valve is shown schematically in FIG. 1. The control slide valve of the power stage is moved to and fro proportionally to the electrical input signal by means of the volume flow by deflecting the pilot stage. The control slide valve then controls exactly the volume flow to a consumer, such as an actuator, connected to the servo valve.
In the previously known servo valves, the valve blocks of the power stage are provided with connection bores and crossholes and the control slide valve sleeve is provided with punctures to transport the hydraulic fluid to the desired interfaces.
Since crossholes and connection bores are applied in the valve blocks of the power stage, the bores subsequently have to be closed from the outside by press-fit plugs or screw plugs to obtain a closed circuit, with hydraulic circuits arising due to the sealing. However, this embodiment of the previously known servo valves has proved to be disadvantageous. Such a servo valve is known from US 2004/0144433 A1.
A further disadvantage of previously known servo valves is that laterally deflected connection punctures have to be provided in the valve block to obtain a transition from the connection bores and crossholes to the control slide valve sleeve. These connection punctures are cut in using a side milling cutter so that grooves arise. However, the arising grooves have a critical fatigue behavior and endurance behavior and, apart from this, have to be deburred in a complex and/or expensive manner.
Furthermore, the valve blocks in the previously known servo valves cannot have a compact construction since sufficient materials have to be present for connection bores and crossholes and also for the press-fit plugs.
A further disadvantage of the known servo valves is that, depending on the system pressure and on the weight limit, the valve blocks are produced from aluminum, titanium or steel, which is very cost-intensive in view of the variety of variants. Additional expenses are also caused by bores for the press-fit plugs, with the plurality of external seals additionally increasing the risk. The higher number of individual parts of the servo valve results in a lower reliability, on the one hand, and in an increase in the manufacturing costs, on the other hand.